The deal with overclocking
In Sandy Bridge processors, one base clock running at 100MHz governs just about everything in the CPU. Changing that base clock in order to raise the core clock speed will cause nearly everything else in the system—PCIe connections, I/O links, and such—to run at the wrong speed, potentially causing all kinds of Very Bad Things to happen. As a result, the bulk of Sandy Bridge overclocking efforts, at least initially, will likely be limited to adjustments of the CPU multiplier. I don't think the CPU was designed this way in order to put the clamps on big, bad overclockers. Instead, I get the impression Sandy Bridge was designed by a team who primarily had mobile applications, like laptops, in mind.

Regardless of what happened there, though, Intel does have a couple of solutions to this dilemma to offer to enthusiasts. The first, obviously, is its K-series processors with unlocked multipliers, including the nicely priced Core i5-2500K at $216—just 11 bucks more than the locked version—and the Core i7-2600K at $317. If you have serious overclocking ambitions in mind and good cooling at your disposal, a K-series CPU will probably be the way to go.

Source: Intel.

Intel is leaving some headroom available to those who opt for a non-K model, as well, in the form of four steps of the multiplier—or 400MHz—above the stock Turbo clock speeds. The example above looks to be a Core i5-2500, with base clock of 3.3GHz, which has Turbo Boost enabled. With the Turbo speed tweaked, it's possible that a single, occupied core could run as fast as 4.1GHz—and all four could run at 3.8GHz. That's a pretty decent amount of headroom left open for "free," I suppose.

I'd expect most users who want a modest amount of overclocking on fairly pedestrian air or water cooling to be satisfied with these arrangements, especially given the pricing of the 2500K. We may be past the days of a $99 bonanza of overclocking headroom, though, as we've seen in some cheap chips from the past. That's kind of a shame. The handful of extreme overclockers out there probably won't be happy at all with the base clock limitations, but they never did represent the average enthusiast's aspirations in such matters.

Sandy and her rivals square off
We have fallen behind a bit in the past six months or so on the CPU reviewing front. We've been so busy covering new technology announcements and such that we've missed out on testing several new speed grades of existing processors, and now is our chance to catch up in a big way, with spiffy new test rigs, a refreshed suite of tests, and a vast array of current and past CPUs to compare. Here's a look at what we've tested.

Model

Cores

Threads

Base core
clock speed

Peak Turbo
clock speed

L3 cache
size

Memory
channels

TDP

Price

Core i3-2100

2

4

3.1 GHz

-

3 MB

2

65 W

$117

Core i5-2400

4

4

3.1 GHz

3.4 GHz

6 MB

2

95 W

$184

Core i5-2500K

4

4

3.3 GHz

3.7 GHz

6 MB

2

95 W

$216

Core i7-2600K

4

8

3.4 GHz

3.8 GHz

8 MB

2

95 W

$317

First, we have a nice selection of Sandy Bridge processors spanning the range of introductory prices, including both of the unlocked K-series chips. Notice that the quad-core parts have 95W TDP ratings, just like most current Lynnfield-based products, yet they incorporate graphics into the mix, as well.

Model

Cores

Threads

Base core
clock speed

Peak Turbo
clock speed

L3 cache
size

Memory
channels

TDP

Price

Pentium G6950

2

2

2.8 GHz

-

3 MB

2

73 W

$87

Core i3-560

2

4

3.33 GHz

-

4 MB

2

73 W

$138

Core i5-655K

2

4

3.2 GHz

3.46 GHz

4 MB

2

73 W

$216

Core i5-760

4

4

2.8 GHz

3.33 GHz

8 MB

2

95 W

$205

Core i7-875K

4

8

2.93 GHz

3.60 GHz

8 MB

2

95 W

$342

Core i7-950

4

8

3.06 GHz

3.33 GHz

8 MB

3

130W

$294

Core i7-970

6

12

3.2 GHz

3.46 GHz

12 MB

3

130 W

$885

Core i7-980X Extreme

6

12

3.33 GHz

3.60 GHz

12 MB

3

130 W

$999

Next, we've tested a pretty broad range of the prior-gen Intel processors spanning from $87 to $999. Many of these chips are newer speed grades, such as the Core i3-560 and Core i5-760, that represent the latest top bin offered in their respective ranges.

We thought we had a beautiful test design when we were putting this plan together, but I have to admit to being snookered by Intel's name conventions on one front: the Core i3-560 and i5-655K are nearly the same thing, with very similar clock frequencies. In fact, the i3-560's base speed is straddled by the i5-655K's base and Turbo speeds. All I can say is that I wanted to represent the most desirable i5-600-series part, and that was definitely the unlocked 655K, in my view. The fact that we had already included nearly the same thing didn't hit me until testing was well underway. There's really no harm done, but that's what happened.

Model

Cores

Threads

Base core
clock speed

Peak Turbo
clock speed

L3 cache
size

Memory
channels

TDP

Price

Athlon II X3 455

3

3

3.3 GHz

-

-

2

95 W

$87

Phenom II X4 840

4

4

3.2 GHz

-

-

2

95 W

$102

Phenom II X2 565 Black

2

2

3.4 GHz

-

6 MB

2

80 W

$115

Phenom II X4 975 Black

4

4

3.6 GHz

-

6 MB

2

125 W

$195

Phenom II X6 1075T

6

6

3.0 GHz

3.5 GHz

6 MB

2

125 W

$199

Phenom II X6 1100T Black

6

6

3.3 GHz

3.7 GHz

6 MB

2

125 W

$265

AMD offers a lot of different CPU models, but its product stack's pricing has been compressed quite a bit by competitive pressures from Intel. After all, you usually can't charge much more for a chip than what your competitor asks for one with similar performance. AMD has still been very active in the context of those limitations, offering 100MHz speed bumps regularly. Three of these CPUs debuted early last month, including the new flagship, the Phenom II X6 1100T, the high-frequency dual-core Phenom II X2 565, and the $87 triple-core Athlon II X3 455. Two more of them are brand-new products being announced today (or very soon) as competition for Sandy Bridge: the Phenom II X4 975, which is a speed bump up to 3.6GHz, and the Phenom II X4 840.

AMD's new Phenoms are here to greet Sandy Bridge

Proving that Intel doesn't have a lock on confusing marketing moves, the Phenom II X4 840 is actually a new entry in AMD's lineup of quad-core chips based on Propus silicon, which lacks an L3 cache. This is not a higher speed version of the Phenom II X4 810, which had a 4MB L3 cache. The logic of AMD's naming scheme to date would dictate that this product would be called the Athlon II X4 650, but marketing has triumphed over logic and given us the newly minted Phenom II X4 840.

Nevertheless, with four cores at 3.2GHz, the X4 840 could prove to be a worthy rival to the new Core i3-2100, and the AMD chip costs less. That logic is a little easier to follow. At around the same price point, the i3-2100 will also face off against the Phenom II X2 565 and its younger sibling, the Core i3-560. Among those, only the Phenom II X2 565 has an unlocked multiplier, as its Black Edition name suggests.

Stepping up a class, we have a six-car pile-up at around $200, with the Core i5-2400 and i5-2500K at the, err, front and rear, to extend the analogy well beyond any reasonable bounds. AMD's brand-new Phenom II X4 975 is smack-dab in the middle at $195, and it's an unlocked Black Edition, making it a pretty direct rival to the also-unlocked Core i5-2500K. If you wish, you could shed a few ticks of clock frequency and opt for more cores at virtually the same price in the form of the Phenom II X6 1075T, whose peak Turbo Core speed is 3.5GHz. Among the older Intel CPUs, the Core i5-760 is the latest entry in its lineup, having supplanted one of our long-time value favorites, the Core i5-750. The two new Sandy Bridge processors will have to contend with all of these rivals in order to prove their worth.

Finally, the Core i7-2600K is as close as the Sandy Bridge processors come to a flagship offering. The Extreme Editions and such will remain the Gulftown six-core parts on the X58 chipset. As $317, the 2600K will essentially replace the Core i7-875K, and it may do unkind things to the quad-core Core i7-950, the cheapest current LGA1366 chip. The only kinda-sorta competition from AMD will be the Phenom II X6 1100T Black Edition, which is somewhat less expensive but similarly unlocked.

All of that covers the current landscape quite well, I believe. For those folks looking to upgrade from an older processor, we have tested three CPUs of historical interest. The first of these is a fun one: the Pentium Extreme Edition 840, one of the very first dual-core PC processors ever. The Pentium EE 840 was the result of the Pentium 4's power and heat problems at higher clock frequencies; it was Intel's first attempt to take advantage of the power efficiency advantages of limiting clock frequency and increasing thread-level parallelism via multiple cores. Thanks to Hyper-Threading, the EE 840 exposes four threads to the operating system and, thanks to its Pentium 4 roots, still runs at a healthy 3.2GHz. Amazingly, the EE 840 installed and ran happily in our Intel X48 chipset-based motherboard. The only accommodation we had to give it was, of course, a larger cooler.

The other two are more recent: a Core 2 Duo E6400, one of the first mid-range variants of the Merom/Conroe architecture and an early value favorite, and a Core 2 Quad Q9400, a reasonably priced quad-core based on 45nm Penryn chips. If your box is rocking one of these processors or something similar, it may be time to upgrade. We'll put these in the context of a wide range of today's CPUs, so you can see what you might get out of taking a step up.